Synthetic resin composition

ABSTRACT

A synthetic resin composition which comprises 20 to 50 parts by weight of olefinic resins, 10 to 40 parts by weight of vinyl chloride resins, and 70 to 10 parts by weight of alumina trihydrate having a gibbsite crystal structure whose average particle size is 30 microns at most.

This invention relates to synthetic resin composition having excellentflameproofness and surface hardness. Mixture of 100 parts by weight ofolefinic polymers such as ethylenic polymers or propylenic polymers withat least 100 parts by weight of various reinforcing inorganic fillersprovides high modulus compositions as set forth in, for example, theJapanese Patent Publication Nos. 8037/65, 28199/71 and 29377/71 and theBritish Pat. No. 936,057.

However, compositions consisting of olefinic polymers and the aforesaidreinforcing inorganic fillers, for example, β-type alumina hydrates, asdisclosed in said Japanese Patent Publication No. 8037/65, provide ahigh modulus product and indeed have great tensile strength andhardness, but low flexibility, tear strength and toughness. Where,however, there are used smaller proportions of an inorganic filler toeliminate the above-mentioned drawbacks, improvement is indeed attainedin flexibility and tear strength but mixing cost rather increases,failing to provide an ecomonically advantageous product. Further,decreased incorporation of an inorganic filler naturally makes itnecessary to use larger amounts of an olefinic polymer. Accordingly,product of such resin composition evolves considerable heat whensubjected to combustion as rubbish after use. Moreover, such productundesirably gives forth large volumes of black smoke or soot during saidcombustion. What is worse, it is readily flammable and unadapted to beused as structural material.

For improvement on the defects of the above-mentioned resin composition,the present inventors found that a resin composition having prominenttoughness, flame retardance, electrical insulation properties, andresistance to chemicals could be produced by blending ethylenic orpropylenic polymers with a relatively large amount (40 to 93 per cent byweight based on the total weight of a resin composition) of α-typealumina trihydrate having a gibbsite crystal structure containing atleast 0.20 per cent by weight of fixed sodium compounds expressed as Na₂O, as disclosed in our Japanese Patent Applications Nos. 28580/72 and31757/72.

The resin compositions set forth in these patent applications exhibitedthe flexibility of olefinic polymers despite the inclusion of arelatively large amount of filler and not only had prominent mechanicalproperties such as tear strength but also presented an extremelyhomogeneous mixed state. However, said resin compositions were stillfound unsatisfactory despite such excellent properties, because themoldings of said resin compositions had too small a surface hardness tobe used as structural material, for example, floors, walls, partitions,and ceilings or inner attachments to automotive wheels. For improvementon the surface hardness of moldings, it may be contemplated to laminateor paint another material on the surface of the moldings, or properlyfinish said surface by printing. However, any of these processes notonly involves complicated steps but also undesirably increases theproduction cost of moldings.

In view of the above-mentioned circumstances, therefore, the object ofthis invention is to provide a synthetic resin composition whosemoldings are prominent not only in surface hardness but also inflameproofness. The synthetic resin composition of this inventioncharacteristically comprises 20 to 50 parts by weight of olefinicresins, 10 to 40 parts by weight of vinyl chloride resins and 70 to 10parts by weight of alumina trihydrate having a gibbsite crystalstructure whose average particle size is 30 microns at most.

As previously mentioned, moldings prepared from the synthetic resincomposition of this invention are prominent not only in surface hardnessand flameproofness but also in mechanical properties such as flexibilityand tear strength, resistance to chemicals and electrical insulationproperties.

It is well known that unless blended with another resin or rubber,olefinic resins (for example, ethylene homopolymer or propylenehomopolymer) and vinyl chloride resins can not be mixed with goodcompatibility. However, incorporation of alumina trihydrate having agibbsite crystal structure, as used in this invention, prominentlyimproves the mixed condition of the above-mentioned olefinic and vinylchloride resins, namely, the surface condition of moldings prepared fromthese two types of resins.

The present inventors have studied various types of olefinic resincompositions containing a large amount of inorganic filler andaccomplished this invention by finding that a resin compositionconsisting of 20 to 50 parts by weight of olefinic resins, 10 to 40parts by weight of vinyl chloride resins and 70 to 10 parts by weight ofalumina trihydrate having a gibbsite crystal structure can providemoldings having prominent surface hardness.

The olefinic resins used in this invention include ethylenic resins andpropylenic resins. The ethylenic resins include ethylene homopolymer,copolymers of at least 80 mol% of ethylene and 20 mol% at most ofanother α-olefin (for example, propylene, or butene-1) and copolymers ofethylene as a main component and a vinyl compound. Particularlypreferred is high density polyethylene (permissively a copolymer ofethylene and 10 mol% at most of another α-olefin) having a melt index of0.001 to 5 g/10 min. as measured at a temperature of 190°C and under aload of 2.16 kg. High density polyethylene is manufactured on anindustrial scale, using a catalytic system (known as the Phillips orstandard type catalyst) mainly consisting of a metal oxide or acatalytic system (known as the Ziegler type catalyst) mainly consistingof a transition metal compound and organo metal compound (generallyorgano aluminium compound) and is already widely applied in variousfields.

On the other hand, the propylenic resins used in this invention includepropylene homopolymer, copolymers (including block copolymers) of atleast 80 mol% of propylene and 20 mol% at most of ethylene or anotherα-olefin (for example, butene-1), and copolymers of propylene as a maincomponent and vinyl compounds or diolefins (for example, butadiene).Preferred is a propylenic polymer whose portion soluble in boilingn-heptane amounts to 40 % at most. Most desired is a propylenic polymerhaving a melt index of 20 g/10 min. as measured at a temperature of230°C and under a load of 2.16 kg. These propylenic resins aremanufactured on an industrial scale, using a catalytic system (known asthe Ziegler-Natta type catalyst) mainly consisting of an organo metalcompound (generally halogenated alkyl aluminium) and a transition metalcompound (for example, titanium trichloride) or an eutectic mixturethereof (for example, a eutectic mixture of titanium trichloride andaluminium chloride [TiCl₃.1/3 AlCl₃ ]) and is already widely accepted invarious fields.

The vinyl chloride resins used in this invention are generally known aspolyvinyl chloride and widely manufactured on an industrial scale. Thevinyl chloride resins include not only vinyl chloride homopolymer butalso a copolymer of at least 85 mol% of vinyl chloride and anothermonomer. Said another monomer includes ethylene, vinylidene chloride,vinyl acetate and acrylic ester. Preferred is a vinyl chloride resinhaving a degree of polymerization of 850 to 1,800. Particularly desiredis a type having a degree of polymerization of 1,000 to 1,400.

The alumina trihydrate having a gibbsite crystal structure [α--Al(OH)₃]which is used in this invention has a monoclinic crystal system. Saidtrihydrate has a crystal structure in which the lattice constant ismeasured as a = 8.62 A, b = 5.06 A and c = 9.70 A, the beta(β) angle isdetermined to be 85°26', and the refractive index is expressed as α=1.568, β= 1.568 and γ= 1.567. This alumina trihydrate is widelymanufactured on an industrial scale (refer to the Japanese PatentPublication No. 5217/54). For the object of this invention, said aluminatrihydrate has an average particle size of 30 microns at most, orpreferably less than 10 microns. If the average particle size exceeds 30microns, then it will be impossible to enable moldings prepared from aresin composition containing such trihydrate to have not only desiredmechanical properties such as flexibility and rigidity but also topresent a satisfactory surface appearance.

As previously mentioned, the synthetic resin composition of thisinvention comprises 20 to 50 parts by weight of olefinic resins, 10 to40 parts by weight of vinyl chloride resins and 70 to 10 parts by weightof alumina trihydrate having a gibbsite crystal structure whose averageparticle size is 30 microns at most. However, said resin composition ispreferred to comprise 20 to 40 parts by weight of olefinic resins, 10 to20 parts by weight of vinyl chloride resins and 70 to 40 parts by weightof alumina trihydrate.

Where the proportion of olefinic resins included in the resincomposition of this invention falls to below 20 parts by weight, thenmoldings prepared from such composition will not only lose a favorablefeeling essentially derived from the olefinic resins, but also becomebrittle. Conversely, where the proportion of the olefinic resins risesabove 50 parts by weight, then resultant moldings will undesirably notonly fail to be improved in surface hardness, but also decrease indimensional stability.

Where the proportion of vinyl chloride resins decreases from 10 parts byweight, then resultant moldings will fail to have satisfactory surfacehardness. Conversely, where said proportion of vinyl chloride resinsincreases over 40 parts by weight, then resultant moldings willundesirably lose a good feeling.

Where alumina trihydrate is used in a smaller proportion than 10 partsby weight, then olefinic resins and vinyl chloride resins will notbecome well miscible, causing resulting moldings not only to present anirregular surface appearance, but also to decrease in selfextinguishingproperty. Conversely, a larger proportion of said trihydrate than 70parts by weight will lead to the low flexibility and brittleness ofresultant moldings.

In practical application, the synthetic resin composition of thisinvention is blended with plasticizers such as phthalic acidderivatives, adipic acid derivatives, azelaic acid derivatives, sebacicacid derivatives, maleic acid derivatives, fumaric acid derivatives,trimellitic acid derivatives, citric acid derivatives, oleic acidderivatives, ricinoleic acid derivatives, stearic acid derivatives,derivatives of other fatty acids, sulfonic acid derivatives, phosphoricacid derivatives, other monoester compounds, glycol derivatives,glycerin derivatives, paraffin derivatives, diphenyl derivatives, epoxyderivatives and polymerization type compounds; lubricants such as higherfatty acid esters, amide compounds and higher alcoholic compounds; andstabilizers such as metallic soaps, salts of inorganic acids andorganotin compounds. These plasticizers, lubricants and stabilizers areused for common vinyl chloride resins.

Though varying with the proportions of vinyl chloride resins andolefinic resins included in the resin composition of this invention, theproportions of the above-mentioned plasticizers, lubricants and/orstabilizers are generally chosen to be 120 parts by weight at most basedon 100 parts by weight of vinyl chloride resins for the plasticizers, 10parts by weight at most based on 100 parts by weight of vinyl chlorideresins for the lubricants and 10 parts by weight at most based on 100parts by weight of vinyl chloride resins for the stabilizers. Though itmay be considered advisable jointly to use the plasticizers andlubricants, yet it is preferred to further add a stabilizer to thesubject resin composition in order to attain its stability.

The above-mentioned phthalic acid derivatives used as plasticizerstypically include dimethyl phthalate, diethyl phthalate, dibutylphthalate, diisobutyl phthalate, diamyl phthalate, dihexyl phthalate,butyl octyl phthalate, butyl isodecyl phthalate, butyl lauryl phthalate,di-(2-ethylhexyl) phthalate, di-n-octyl phthalate, butyl coconut alkylphthalate, dilauryl phthalate, diheptyl phthalate, diisooctyl phthalate,octyl decyl phthalate, n-octyl.n-decyl phthalate, diisodecyl phthalate,ditridecyl phthalate, ethyl hexyl decyl phthalate, dinonyl phthalate,butyl benzyl phthalate, dicyclohexyl phthalate, diallyl phthalate,dimethoxyethyl phthalate, dibutoxyethyl phthalate, methyl phthalyl ethylglycolate and butyl phthalyl butyl glycolate.

The adipic acid derivatives used as plasticizers typically includedi-n-butyl adipate, diisobutyl adipate, di-(2-ethyhexyl) adipate,diisooctyl adipate, diisodecyl adipate, octyl decyl adipate, dicapryladipate, benzyl-n-butyl adipate, polypropylene adipate, dibutoxyethyladipate and benzyl octyl adipate.

The azelaic acid derivatives used as plasticizers typically includedi-(2-ethylhexyl) azelate, diisooctyl azelate,di-2-ethylhexyl-4-thioazelate, di-n-hexyl azelate and diisobutylazelate.

The sebacic acid derivatives used as plasticizers typically includedimethyl sebacate, dibutyl sebacate, di-(2-ethylhexyl) sebacate, anddiisooctyl sebacate.

The maleic acid derivatives used as plasticizers typically includedi-n-butyl maleate, dimethyl maleate, di-(2-ethylhexyl) maleate anddinonyl maleate.

The fumaric acid derivatives used as plasticizers typically includedibutyl fumarate and di-(2-ethylhexyl) fumarate.

The trimellitic acid derivatives used as plasticizers typically includetri-(2-ethylhexyl) trimellitate, triisodecyl trimellitate,n-octyl.n-decyl trimellitate, triisooctyl trimellitate and diisooctylmonoisodecyl trimellitate.

The citric acid derivatives used as plasticizers typically includetriethyl citrate, tri-n-butyl citrate, acetyl triethyl citrate, acetyltri-n-butyl citrate, acetyl tri-n-octyl n-decyl citrate and acetyltri-(2-ethylhexyl) citrate.

The oleic acid derivatives used as plasticizers typically include methyloleate, butyl oleate, methoxyethyl oleate, tetrahydrofurfuryl oleate,glyceryl oleate and diethylene glycol monooleate.

The ricinoleic acid derivatives used as plasticizers typically includemethyl acetyl ricinoleate, butyl acetyl ricinoleate, glycerylmonoricinoleate, diethylene glycol monoricinoleate, glyceryl tri-(acetylricinoleate) and alkyl acetyl ricinoleate.

The stearic acid derivatives used as plasticizers typically includen-butyl stearate, glyceryl monostearate, diethylene glycol distearateand chlorinated methyl stearate.

Other fatty acid derivatives used as plasticizers typically includediethylene glycol dipelargonate, diethylene glycol monolaurate and butylcellosolve pelargonate.

The sulfonic acid derivatives used as plasticizers typically includebenzene sulfonic acid butylamide, O-toluene sulfonamide,N-ethyl-p-toluene sulfonamide, O-toluene ethyl sulfonamide andN-cyclohexyl-p-toluene sulfonamide.

The phosphoric acid derivatives used as plasticizers typically includetriethyl phosphate, tributyl phosphate, tri-(2-ethylhexyl) phosphate,triphenyl phosphate, cresyl diphenyl phosphate, tricresyl phosphate,tritolyl phosphate, trixylyl phosphate, tris (chloroethyl) phosphate,diphenyl mono-O-xenyl phosphate and diphenyl xylenyl phosphate. Othermonoester compounds used as plasticizers typically includediphentaerythritol ester and fatty acid esters of pentaerythritol.

The glycol derivatives used as plasticizers typically includetriethylene glycol di-(2-ethylbutyrate), triethylene glycoldi-(2-ethylhexoate), dibutyl methylene bis-thioglycolate, polyethyleneglycol and polyglycol ether.

The glycerin derivatives used as plasticizers typically include glycerolmonoacetate, glycerol diacetate, glycerol tributyrate, glyceroltripropionate and glycerol ether acetate.

The epoxy derivatives used as plasticizers are broadly divided intoepoxidized unsaturated fats and oils, epoxidized unsaturated fatty acidesters and epoxidized cyclohexane derivatives.

The polymerization type compounds used as plasticizers typically includepolyesters having a molecular weight of 1,000 to 8,000, polyethershaving a viscosity of 600 to 1,000 centipoises at 25°C, andacrylonitrile-butadiene copolymer.

The higher fatty acid esters used as lubricants typically include butylstearate and methyl hydroxystearate.

The amide compounds used as lubricants typically include stearoamide,methylene bis-stearoamide, hydroxy stearic acid ethylene diamide,hydroxystearic acid methylolamide, hydroxystearic acid oleylamide andhydroxystearic acid erucylamide.

The higher alcohol compounds used as lubricants typically includestearyl alcohol. Other lubricants include high melting wax.

The metallic soaps used as stabilizers typically include lithiumstearate, magnesium stearate, calcium stearate, calcium chlorostearate,calcium laurate, strontium stearate, barium stearate, bariumchlorostearate, barium laurate, barium 2-ethylhexylate, bariumricinoleate, zinc stearate, zinc laurate, cadmium stearate, cadmiumlaurate, cadmium ricinoleate, lead stearate, dibasic lead stearate, lead2-ethylhexylate, tribasic lead maleate, dibasic lead phthalate and leadsalicylate.

The salts of inorganic acids used as stabilizers typically include alkylaryl cadmium phosphite, basic lead silicate, tribasic lead sulfate,basic lead sulfite and dibasic lead phosphite.

The organotin compounds used as stabilizers typically include dibutyltin dilaurate, dibutyl tin maleate, dibutyl tin laurate-maleate complex,dimethyl tin compounds, actyl tin compounds and stamic diol derivatives.

The above-listed plasticizers, lubricants and stabilizers are alreadycommercially available generally in the form blended with vinyl chlorideresins. Such marketed vinyl chloride resins may be directly used as acomponent of the synthetic resin composition of this invention.

Where the above-mentioned additives to vinyl chloride resins are used ina larger proportion than 120 parts by weight based on 100 parts byweight of vinyl chloride resins, then the resultant resin compositionwill undesirably present a sticky state.

Though it is possible to use only one kind of the aforesaidplasticizers, lubricants and stabilizers respectively, yet it isgenerally preferred to use two or more kinds of these respectiveadditives.

The synthetic resin composition of this invention may be prepared byfirst mixing two or three components of olefinic resins, vinyl chlorideresins, alumina trihydrate and additives to the vinyl chloride resinsand thereafter adding the remaining component or components. However, itis also possible to mix together all said four components at once. It isadvised to carry out said mixing by a mechanical mixing process using aroll mill, Banbury mixer or melt extruder commonly used in the syntheticresin industry.

The synthetic resin composition of this invention prepared by mixing thecomponents by any of the above-mentioned processes can be formed intovarious forms such as films, boards, sheets, pipes, rods, etc. by meansof, for example, calender molding, injection molding or extrusionmolding. However, the temperature at which final moldings aremanufactured is desired to range between 150° and 300°C, or mostpreferably between 180° and 250°C.

Moldings prepared from the synthetic resin composition of this inventionare not only excellent in mechanical properties such as impactresistance and flexibility despite inclusion of a relatively largeamount of alumina trihydrate, but also have prominent heat stability andare moreover flame retardant. Further, since the subject resincomposition contains a small proportion of olefinic resins, moldingsthereof not only evolve relatively small volumes of black smoke (soot)when fired for dumping after use, but also release little heat.

Moldings of the synthetic resin composition of this invention can bebonded with metals such as aluminium, iron, copper and tin, alloysthereof (for example, brass and stainless steel), cellulosic materialssuch as paper, fibers and wood and inorganic materials such as stone,gypsum plaster and cement by interposing an adhesive material betweenboth groups of objects of bonding or by previously incorporatingadhesive compounds such as unsaturated carboxylic acid or organicperoxide in the subject resin composition itself.

The above-mentioned unsaturated carboxylic acid in liquid form includesacrylic acid, methacrylic acid and monomethyl 2-methylene glutarate. Theunsaturated carboxylic acid in solid form includes crotonic acid, maleicacid, fumaric acid, itaconic acid, 2-methylene glutaric acid andcitraconic acid.

Though addition of 0.1 to 4.0 parts by weight of said unsaturatedcarboxylic acid, whether in liquid or solid form, to the resincomposition of this invention based on 100 parts by weight thereofappreciably improves the adhesivity of said composition, yet furtherincorporation of 0.01 to 0.2 part by weight of organic peroxide based on100 parts by weight of the subject resin composition more prominentlyelevates its adhesivity. Firm bonding between moldings of said resincomposition and the articles of other materials can be effected bycoating the liquid unsaturated carboxylic acid on the surface of themoldings of said resin composition at the rate of 1 to 2 mg/cm²,followed by heating and pressure. However, application of the aforesaidproportion of organic peroxide to the subject resin composition inaddition to the liquid unsaturated carboxylic acid noticeably increasesthe adhesivity of said resin composition.

The above-mentioned peroxide includes ketone peroxide such as1,1-bis-tert-butyl peroxy-3,3,5-trimethyl cyclohexane; hydroperoxidesuch as 2,5-dimethyl hexane-2,5-dihydroperoxide; dialkyl peroxide suchas dicumyl peroxide; diacyl peroxide such as benzoyl peroxide; andperoxyester such as 2,5-dimethyl-2,5-dibenzoyl peroxyhexane.

Moldings of the resin composition of this invention and the articles ofother materials can be properly bonded together by applying atemperature of 140° to 180°C and a low pressure for 2 to 10 minutes. Inthis case, the articles of other materials may take various forms suchas films, sheets, foils, fabrics, powders, boards, pipes, rod, etc.

Depending on the uses of moldings of the resin composition, the resincomposition of this invention normally comprising olefinic resins, vinylchloride resins and alumina trihydrate and, if required, additives tosaid vinyl chloride resins may be blended with other resins. Further,the resin composition of this invention may contain other additivesgenerally used with olefinic resins, such as a stabilizer to light(ultraviolet ray), oxygen, ozone and heat, flame retardant, inhibitor ofdeterioration by metal (for example, copper inhibitor), reinforcingagent, filler, plasticizer, coloring agent, colorability promotor,antistatic agent, decomposition accelerator and electric propertyimprover.

Moldings prepared from the synthetic resin composition of this inventionare excellent, as previously described, not only in surface hardness andflame retardance, but also heat stability and flexibility, and can befavorably used in wide fields in various forms, for example, in the formof sheets or boards or a combination thereof as outer structural membersand materials for automobiles, shipping and industrial applications.

This invention will be more fully understood by reference to theexamples and controls which follow. Throughout the examples andcontrols, the surface hardness of moldings was determined by the pencilscratch test specified in the Japanese Industrial Standard (JIS) K 5400.Namely, said determination was made on a pencil scratch tester which wasdesigned to indicate the surface hardness of moldings in the maximumhardness of the lead of a pencil which could scratch the surface of asample molding under a load of 50 g without marking any scar thereon.The selfextinguishing property was determined on the basis of the oxygenindex pursuant to the JIS K 7201. The tear strength was determined byobtaining the Elemendorf value according to the JIS P 8116. The feelingwas expressed in the terms "dry," "sticky," "soft" and "hard" used indenoting the senses experimentally derived from the hand touch inconjunction with the corresponding values of the Sward rocker hardness.Namely, the Sward rocker hardness was determined according to the JIS K5640 on the basis of 50 shakings of the Sward rocker on the standardglass plate which was taken as the Sward rocker hardness of 100. Thedimensional stability was tested by cutting off a piece 150 mm long and6 mm wide from a sheet-like sample molding at room temperature, leavingthe cut piece 10 minutes in a circulating thermostat at 120°C andthereafter cooling the piece with ice and determining the ratio whichthe extension or shrinkage of the piece bears to the original length of150 mm. The peel strength of the bonded mass was determined by peelingthem through an angle of 180° at a tensile speed of 100 mm/min. pursuantto ASTM D903-49.

EXAMPLE 1

25 parts by weight of high density polyethylene having a density of 0.94g/cc and a melt index of 0.05 g/10 min. as measured at a temperature of190°C and under a load of 2.16 kg (manufactured by Showa Yuka K.K. undera trade name "Sholex"), 50 parts by weight of alumina trihydrate havinga gibbsite crystal structure with an average particle size of 6 micronsand 25 parts by weight of polyvinyl chloride containing 25 % by weightof dioctyl phthalate (said polyvinyl chloride contains 5 mol% ofethylene and has an average degree of polymerization of 1050.) werekneaded together about 5 minutes on an 8-inch mixing roll whose surfacetemperature was set at 160°C to provide a sheet 0.2 mm thick. A pencilscratch test made of the surface hardness of said sheet showed that thesurface hardness of said sheet was a pencil hardness of the B grade. Thesheet indicated desirably small changes in dimensional stability, as-0.33 % in the longitudinal direction (the direction in which the mixingroll rotated in forming the sheet) and +0.05 % in the lateral direction.The sheet was selfextinguishing with an oxygen index of 22.1 and had atear strength of 7.3 kg/cm in the longitudinal direction and a tearstrength of 5.5 kg/cm in the lateral direction. Further the sheetsatisfactorily felt "soft and dry" with a Sward rocker hardness of 8.

CONTROL 1

55 parts by weight of high density polyethylene, 40 parts by weight ofalumina trihydrate and 5 parts by weight of polyvinyl chloride all ofthe same kind as in Example 1 were kneaded together in the same manneras in Example 1 to form a sheet. The pencil scratch test showed that thesheet had a surface hardness of the 4B grade expressed in the hardnessof the lead of the pencil. Further, the sheet presented prominentvariations in dimensional stability, namely, -5.4 % in the longitudinaldirection and -2.1 % in the lateral direction.

CONTROL 2

47 parts by weight of high density polyethylene, 8 parts by weight ofalumina trihydrate and 45 parts by weight of polyvinyl chloride all ofthe same kind as in Example 1 were kneaded together in the same manneras in Example 1 to provide a sheet. The sheet was flammable with anoxygen index of 19.2. Further, the sheet undesirably felt rigid with aSward rocker hardness of 16.

CONTROL 3 CONTROL 3

15 parts by weight of high density polyethylene, 75 parts by weight ofalumina trihydrate and 10 parts by weight of polyvinyl chloride all ofthe same kind as in Example 1 were kneaded together in the same manneras in Example 1 to form a sheet. The sheet was brittle with a tearstrength of 0.8 kg/cm in the longitudinal direction and a tear strengthof 0.5 kg/cm in the lateral direction.

EXAMPLE 2

The polyvinyl chloride of Example 1 containing dioctyl phthalate wasreplaced by the type containing 5 % by weight of glyceryl monostearate.Thus substantially the same three components as in Example 1 werekneaded together in the same manner as shown in Example 1 to provide asheet. The sheet had a surface hardness of the H grade expressed in thehardness of the lead of the pencil in the pencil scratch test. Further,the sheet was selfextinguishing with an oxygen index of 23.6 and had atear strength of 5.3 kg/cm in the longitudinal direction and a tearstrength of 4.8 kg/cm in the lateral direction. The sheet desirably felt"dry and soft" with a Sward rocker hardness of 6.

EXAMPLE 3

The polyvinyl chloride in Example 1 containing dioctyl phthalate wasreplaced by the type containing 1.5 % by weight of calcium stearate.Thus substantially the same three components as in Example 1 werekneaded together in the same manner as in Example 1 to provide a sheet.The sheet had a surface hardness of the H grade expressed in thehardness of the lead of the pencil in the pencil scratch test. The sheetindicated small changes in dimensional stability, as -0.29 % in thelongitudinal direction and +0.05 % in the lateral direction. Further,the sheet was selfextinguishing with an oxygen index of 23.6, and had atear strength of 8.2 kg/cm in the longitudinal direction and a tearstrength of 6.6 kg/cm in the lateral direction. The sheet also felt"dry" with a Sward rocker hardness of 8.

EXAMPLE 4

Kneading was carried out in the same manner as in Example 1 to form asheet, excepting that the polyvinyl chloride used in Example 1 wasreplaced by the type which did not contain dioctyl phthalate. The sheetthus prepared had a surface hardness of the 2H grade expressed in thehardness of the lead of the pencil in the pencil scratch test. The sheetdesirably indicated small changes in dimensional stability as -0.25 % inthe longitudinal direction and +0.05 % in the lateral direction. Thesheet was also selfextinguishing with an oxygen index of 24.1 and a tearstrength of 8.5 kg/cm in the longitudinal direction and a tear strengthof 6.2 kg/cm in the lateral direction. The sheet favorably felt "softand dry" with a Sward rocker hardness of 8.

EXAMPLE 5

The high density polyethylene of Example 1 was replaced by crystallinepropylene homopolymer having a density of 0.89 g/cc, melt flow index of2.0 g/10 min. as measured at a temperature of 230°C and under a load of2.16 kg and containing 17 % of boiling n-heptane-soluble portion(manufactured by Showa Yuka K.K. under a trade name "Shoallomer"). Thussubstantially the same three components as in Example 1 were kneadedtogether in the same manner as in Example 1 to form a sheet. The sheethad a surface hardness of the 2H grade expressed in the hardness of thelead of the pencil in the pencil scratch test. The sheet presented smallchanges in dimensional stability, as -0.05 % in the longitudinaldirection and +0.05 % in the lateral direction. The sheet wasselfextinguishing with an oxygen index of 22.4, and had a tear strengthof 2.9 kg/cm in the longitudinal direction and a tear strength of 2.1kg/cm in the lateral direction. The sheet desirably felt "dry" with aSward rocker hardness of 8.

EXAMPLE 6

35 parts by weight of high density polyethylene, 50 parts by weight ofalumina trihydrate and 15 parts by weight of polyvinyl chloride, allused in Example 1, were kneaded together in the same manner as inExample 1 to form a sheet. The sheet had a surface hardness of the Bgrade expressed in the hardness of the lead of the pencil in the pencilscratch test. The sheet indicated small variations in dimensionalstability, as -0.05 % in the longitudinal direction and +0.05% in thelateral direction. The sheet was selfextinguishing with an oxygen indexof 22.4, and had a tear strength of 9.7 kg/cm in the longitudinaldirection and a tear strength of 7.6 kg/cm in the lateral direction. Thesheet favorably felt "dry" with a Sward rocker harndess of 10.

EXAMPLE 7

25 parts by weight of high density polyethylene used in Example 1, 60parts by weight of alumina trihydrate used in Example 1 and 15 parts byweight of vinyl chloride homopolymer having an average degree ofpolymerization of 1400 were kneaded together in the same manner as inExample 1 to form a sheet. The sheet had a surface hardness of the Hgrade expressed in the hardness of the lead of the pencil in the pencilscratch test. The sheet showed small changes in dimensional stability,as -0.21 % in the longitudinal direction and +0.05 % in the lateraldirection. The sheet was selfextinguishing with an oxygen index of 23.5and had a tear strength of 7.0 kg/cm in the longitudinal direction and atear strength of 4.5 kg/cm in the lateral direction. The sheet desirablyfelt "dry" with a Sward rocker hardness of 6.

EXAMPLE 8

45 parts by weight of high density polyethylene, 40 parts by weight ofalumina trihydrate and 15 parts by weight of polyvinyl chloride, allused in Example 1, were kneaded together in the same manner as inExample 1 to provide a sheet. The sheet had a surface hardness of the Hgrade expressed in the hardness of the lead of the pencil in the pencilscratch test. The sheet indicated small variations in dimensionalstability, as -0.54 % in the longitudinal direction and +0.05 % in thelateral direction. The sheet was selfextinguishing with an oxygen indexof 20.2, and had a tear strength of 8.4 kg/cm in the longitudinaldirection and a tear strength of 5.6 kg/cm in the lateral direction. Thesheet favorably felt "dry" with a Sward rocker hardness of 10.

EXAMPLE 9

40 parts by weight of high density polyethylene, 40 parts by weight ofalumina trihydrate and 20 parts by weight of polyvinyl chloride, allused in Example 1, were kneaded together in the same manner as inExample 1 to form a sheet. The sheet had a surface hardness of the 2Bgrade expressed in the hardness of the lead of the pencil in the pencilscratch test. The sheet presented small variations in dimensionalstability, as -0.54 % in the longitudinal direction and +0.05 % in thelateral direction. The sheet was selfextinguishing with an oxygen indexof 20.7, and had a tear strength of 6.3 kg/cm in the longitudinaldirection and a tear strength of 3.1 kg/cm in the lateral direction. Thesheet desirably felt "dry" with a Sward rocker hardness of 10.

EXAMPLE 10

33.3 parts by weight of high density polyethylene having a density of0.95 g/cc and a melt index of 0.03 g/10 min, 33.3 parts by weight ofalumina trihydrate used in Example 1 and 33.3 parts by weight ofpolyvinyl chloride used in Example 1, were kneaded together in the samemanner as in Example 1 to provide a sheet. The sheet had a surfacehardness of the B grade expressed in the hardness of the lead of thepencil in the pencil scratch test. The sheet showed small changes indimensional stability, as -1.2 % in the longitudinal direction and -0.09% in the lateral direction. The sheet was selfextinghishing with anselfextinguishing index of 21.0, and had a tear strength of 6.0 kg/cm inthe longitudinal direction and a tear strength of 3.9 kg/cm in thelateral direction. The sheet desirably felt "dry" with a Sward rockerhardness of 10.

EXAMPLE 11

30 parts by weight of high density polyethylene, 40 parts by weight ofalumina trihydrate and 30 parts by weight of polyvinyl chloride, allused in Example 1, were kneaded together in the same manner as inExample 1 to form a sheet. The sheet had a surface hardness of the HBgrade expressed in the hardness of the lead of the pencil in the pencilscratch test. The sheet presented small variations in dimensionalstability, as -0.55 % in the longitudinal direction and +0.05 % in thelateral direction. The sheet was selfextinguishing with an oxygen indexof 21.5, and had a tear strength of 5.1 kg/cm in the longitudinaldirection and a tear strength of 2.3 kg/cm in the lateral direction. Thesheet favorably felt "soft" with a Sward rocker hardness of 8.

EXAMPLE 12

25 parts by weight of high density polyethylene, 55 parts by weight ofalumina trihydrate and 20 parts by weight of polyvinyl chloride, allused in Example 1, were kneaded together in the same manner as inExample 1 to form a sheet. The sheet had a surface hardness of the HBgrade expressed in the hardness of the lead of the pencil in the pencilscratch test. The sheet indicated small variations, as -0.19 % in thelongitudinal direction and +0.05 % in the lateral direction. The sheetwas selfextinguishing with an oxygen index of 23.0, and had a tearstrength of 5.3 kg/cm in the longitudinal direction and a tear strengthof 2.3 kg/cm in the lateral direction. The sheet satisfactorily felt"dry" with a Sward rocker hardness of 8.

EXAMPLE 13

The polyvinyl chloride used in Example 1 was replaced by the typecontaining 40 % by weight of dioctyl phthalate. Thus substantially thesame three components as in Example 1 were kneaded together in the samemanner as in Example 1 to provide a sheet. The sheet had a surfacehardness of the 2B grade expressed in the hardness of the lead of thepencil in the pencil scratch test. The sheet was selfextinguishing withan oxygen index of 22.0, and had a tear strength of 8.0 kg/cm in thelongitudinal direction and a tear strength of 6.0 kg/cm in the lateraldirection. The sheet desirably felt "soft" with a Sward rocker hardnessof 6.

EXAMPLE 14

The polyvinyl chloride used in Example 1 was replaced by the typecontaining 25 % by weight of dioctyl phthalate and 3 % by weight ofbutyl stearate. Thus substantially the same three components as inExample 1 were kneaded together in the same manner as in Example 1 toform a sheet. The sheet had a surface hardness of the B grade expressedin the hardness of the lead of the pencil in the pencil scratch test.The sheet showed small variations in dimensional stability, as -0.30 %in the longitudinal direction and +0.10 % in the lateral direction. Thesheet was selfextinguishing with an oxygen index of 22.1, and had a tearstrength of 7.5 kg/cm in the longitudinal direction and a tear strengthof 6.0 kg/cm in the lateral direction. The sheet satisfactorily felt"soft and dry," with a Sward rocker hardness of 6.

EXAMPLE 15

25 parts by weight of high density polyethylene having a density of 0.96g/cc and a melt index of 1.5 g/10 min, 50 parts by weight of aluminathrihydrate having an average particle size of 1.2 microns and 25 partsby weight of polyvinyl chloride used in Example 1 were kneaded togetherin the same manner as in Example 1 to form a sheet. The sheet had asurface hardness of the HB grade expressed in the hardness of the leadof the pencil in the pencil scratch test. The sheet indicated smallchanges in dimensional stability, as -0.29 % in the longitudinaldirection and +0.04 % in the lateral direction. The sheet wasselfextinguishing with an oxygen index of 23.1, and had a tear strengthof 9.3 kg/cm in the longitudinal direction and a tear strength of 7.2kg/cm in the lateral direction. The sheet desirably felt "dry" with aSward rocker hardness of 8.

EXAMPLE 16

Kneading was carried out in the same manner as in Example 1, exceptingthat the resin composition of Example 1 was further blended with 3 partsby weight of fumaric acid, thereby forming a sheet about 3.0 mm thick.The sheet was placed between two 0.08 mm thick aluminium foils (JISH-4191) whose surface was previously washed and degreased bytrichloroethylene. The superposed mass was pressed together for 5minutes at a temperature of 160°C and a pressure of 50 kg/cm², followedby cooling to room temperature using a water-cooled press at a pressureof 50 kg/cm². The bonded mass thus obtained had a peel strength of 9.3kg/2.5 cm width.

EXAMPLE 17

Kneading was effected in the same manner as in Example 16 to form asheet, excepting that the amounts of high density polyethylene, aluminatrihydrate and polyvinyl chloride used in Example 16 were changed to 20,70 and 10 parts by weight respectively. The sheet was placed between twoaluminium foils of the same type as in Example 16, followed bycompression under heat in the same manner as in Example 16. The bondedmass had a peel strength of 8.3 kg/2.5 cm width.

EXAMPLE 18

The resin composition of Example 16 which was further blended with 0.05part by weight of dicumyl peroxide was kneaded in the same manner as inExample 16 to form a sheet. The sheet was placed between two aluminiumfoils of the same type as in Example 16, followed by compression underheat in the same manner as in Example 16. The bonded mass had a peelstrength of 11.5 kg/2.5 cm width.

EXAMPLE 19

The two aluminium foils used in Example 16 were replaced by two 0.2 mmthick galvanized sheets whose surface was previously degreased bytrichloroethylene. A sheet obtained by kneading the resin composition ofExample 16 was placed between said galvanized sheets. The superposedmass was pressed together under heat in the same manner as in Example16. The bonded mass had a peel strength of 8.5 kg/2.5 cm width.

EXAMPLE 20

The two aluminium foils used in Example 16 were replaced by two piecesof kraft paper. A sheet obtained by kneading the resin composition ofExample 16 was placed between said pieces of kraft paper. The superposedmass was pressed together under heat in the same manner as in Example16. The bonded mass had a peel strength of 8.5 kg/2.5 cm width. (Thekraft paper was torn off due to the firm bonding of said superposedmass.)

What we claim is:
 1. A synthetic resin composition capable of formingmoldings with good surface hardness and flame resistance consistingessentially of 20 to 50 parts by weight of olefinic resin, 10 to 40parts by weight of vinyl chloride resin and 70 to 10 parts by weight ofalumina trihydrate of the formula α-Al(OH)₃ with a gibbsite crystalstructure in which the lattice constant is measured as a = 8.62A, b =5.06A and c = 9.70A, the β (B) angle is determined to be 85°26' and therefractive index is expressed as α = 1.568, β = 1.568 and γ = 1.567 andwhich has an average particle size under 30 microns, said olefinic resinbeing selected from the group consisting of ethylene homopolymer,copolymers formed of at least 80 mol% ethylene and not over 20 mol% ofother α-olefin, propylene homopolymers and copolymers formed of at least80 mol% propylene and not over 20 mol% of other α-olefin or diolefin,and said vinyl choride resin being selected from the group consisting ofvinyl chloride polymer and mixtures thereof with up to 120 parts byweight of plasticizer, up to 10 parts by weight of lubricant and up to10 parts by weight of stabilizer per 100 parts of vinyl chloridepolymer, said vinyl chloride polymer having a degree of polymerizationbetween about 850 to 1,800 and being selected from the group consistingof vinyl chloride homopolymer and copolymers formed of at least 85 mol%vinyl chloride with ethylene, vinylidene chloride, vinyl acetate oracrylic ester.
 2. A synthetic resin composition according to claim 1wherein said alumina trihydrate contains at least 0.20 percent by weightof fixed sodium compounds expressed as Na₂ O.
 3. The composition ofclaim 1 wherein said olefinic resin is high density polyethylene havinga melt index of 0.001 to 5 g/10 min. measured at 190°C under a load of2.16 kg.
 4. The composition of claim 1 wherein said olefinic resin ispolypropylene having a melt index of about 20 g/10 min. measured at230°C under a load of 2.16 kg.
 5. The composition of claim 1 whichcontains 0.1 to 4.0 parts by weight of unsaturated carboxylic acid basedon 100 parts by weight of said resin composition.
 6. The composition ofclaim 1 which contains 0.01 to 0.2 parts by weight of organic peroxidebased on 100 parts by weight of said resin composition.
 7. A syntheticresin composition according to claim 5 wherein the unsaturatedcarboxylic acid is one selected from the group consisting of acrylicacid, methacrylic acid, monomethyl 2-methylene glutarate, crotonic acid,maleic acid, fumaric acid, itaconic acid, 2-methylene glutaric acid andcitraconic acid.
 8. A synthetic resin composition according to claim 6wherein the organic peroxide is one selected from the group consistingof ketone peroxide, hydroperoxide, dialkyl peroxide, diacyl peroxide andperoxyester.